Attempt four at landing the "histogram.h removed from message_loop.h" patch.

chrome/browser/io_thread.h

 // Copyright (c) 2010 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_BROWSER_IO_THREAD_H_
 #define CHROME_BROWSER_IO_THREAD_H_
 
 #include <vector>
 
 #include "base/basictypes.h"
 #include "base/ref_counted.h"
 #include "base/scoped_ptr.h"
-#include "base/task.h"
 #include "chrome/browser/browser_process_sub_thread.h"
 #include "chrome/browser/net/chrome_network_delegate.h"
 #include "chrome/common/net/predictor_common.h"
 #include "chrome/browser/net/connect_interceptor.h"
 #include "net/base/host_resolver.h"
 #include "net/base/network_change_notifier.h"
 
 class ChromeNetLog;
 class ListValue;
 
@@ skipping 88 matching lines @@
   // these observers would be used accidentally after we have begun to tear
   // down.
   chrome_browser_net::ConnectInterceptor* speculative_interceptor_;
   net::HostResolver::Observer* prefetch_observer_;
   chrome_browser_net::Predictor* predictor_;
 
   DISALLOW_COPY_AND_ASSIGN(IOThread);
 };
 
 #endif  // CHROME_BROWSER_IO_THREAD_H_